Since I did my exhaust with the addition of ELH, up pipe, and catless devorced DP I have noticed some different sounds. I am trying to decipher between the "new" sounds of the exhaust and what the engine is doing. I have noticed when I start my car when it is cold in the morning or after work there is some sort of air pressure/fan noise that turns on for ~15 seconds (it may be the air pump for that matter, I know the 2012 WRX has one). Under this condition for the first 15 seconds, I can hear a gurgling popping noise in the exhaust like small backfires which sparked my questions. What actually is it (if its not the air pump)? What does it do? Does it ever come on except for cold starts?